1. Field of the Invention
This invention relates to slurry borehole mining and more particularly to a method and apparatus for changing the tool function from drilling to mining without removing the tool from the wellbore.
2. Description of the Prior Art
Hydraulic borehole mining of ore is broadly known in the art as evidenced by the following U.S. Patents:
U.S. Pat. Nos. 3,155,177 and 3,316,985 issued by A. B. Fly on Nov. 3, 1964 and May 2, 1967 respectfully teach a method and apparatus for slurry mining through a borehole which may be changed between its drilling mode of operation and its mining mode of operation without removing the tool from the borehole. The invention teaches the essential controls needed to convert from drilling to mining, i.e., mining nozzle flow, eductor nozzle flow and fluid flow to the drill bit each with a drilling mode and a mining mode of operation. Electric motors within the tool string operate the valves to convert the apparatus from the drilling mode to the mining mode of operation while the tool is still in the borehole.
U.S. Pat. Nos. 3,730,592 issued May 1, 1973 and 3,747,696 issued July 24, 1973 to Wenneborg et al discloses a method and apparatus for borehole mining wherein a hydraulic actuating force for changing the function of the tool from drilling to mining is transmitted from the surface and the actuating fluid line is located wholly within the fluid supply passage to the lower tool section; the hydraulic valve operating means is used to operate the mining nozzle, foot valve and a slurry eductor located at the base of the tool.
U.S. Pat. No. 4,035,023 filed July 15, 1975 and issued July 12, 1977 to Clifford Cockrell discloses a hydraulically operated foot valve which controlls the volume of slurry rising to the surface and is operated by the differential pressure between the vented cavity pressure at the base of the tool and the hydraulic pressure supplied by a slurry level controller.
In this disclosure Cockrell is the first to teach a principle of self-activating down-hole hydraulic valves for tool control; he is first to disclose, describe and use the differential pressure between a control pressure equivalent to or less than system pressure and the vented cavity pressure to establish a hydraulic actuating force for down-hole hydraulic valve control. Cockrell is also first to teach, describe and use the differential hydraulic actuating force between a control pressure and the cavity pressure to modulate down-hole control valves.
U.S. Pat. No. 4,059,166 of Nov. 22, 1977 and No. 4,067,617 of Jan. 10, 1978 issued to P. R. Bunnelle disclose an apparatus for slurry mining wherein several different hydraulic control systems are disclosed to convert the down-hole tool from drilling to mining all with valve control means located within the fluid supply passage to the tool. A control system employing a conduit extending to the surface is used to hydraulically modulate the eductor nozzle to control the cavity pressure control systems activated by the difference between the pump pressure and a vented or cavity pressure are also employed. Self-activating systems to modulate the eductor nozzle also employ the pressure difference between a control pressure and a vented cavity pressure for valve actuation. Seperate control systems are employed for the eductor and the foot valve. An important feature of these systems is that the valve actuating control pressure and the drilling system pressure are the same during drilling while during mining the valve actuating control pressure is established by venting to the cavity pressure or to the atmosphere.
U.S. Pat. No. 4,077,671 of Mar. 7, 1978 and No. 4,077,481 of Mar. 7, 1978 issued to P. R. Bunnelle discloses a modified valve control system which is self-activating by responding to the pressure differential between the system pressure and the pressure in the well cavity. A "vented" control fluid is supplied for selectively opening or closing valves which acts in opposition to the fluid at system pressure on the control means to change the tool function. The salient feature of this method is that during the drilling mode the valve actuating control pressure and the drilling pressure are the same while during mining the valve actuating control pressure is established by venting to the cavity pressure or to the atmosphere.
U.S. Pat. No. 4,344,491 issued Aug. 17, 1982 to J. J. Nolan and J. E. Coakley discloses a valve actuating mechanism actuated by the pressure differential between the drilling system pressure and the mining system pressure. System or pumping pressure is applied to both sides of the piston of a power cylinder with the rod attached to the valve handle. The actuating force being supplied by the differential area of pressure on each side of the piston. The basis for a differential area of pressure being a reduced area on the rod side of the piston which has only the pressure within the discharge conduit acting on the rod extending through the cylinder.
A resilient spring within the cylinder holds the piston in the drilling mode during the application of drilling pressure; the application of mining system pressure forces the piston against the urging of the spring toward and against the stop within the cylinder actuating the valve. An orifice in the tubing connecting each end of the cylinder controls the rate of travel of the piston. The valve actuators use only the pump or system pressure to actuate the valves.